Deep Sky Remote Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Sky Remote Observatory clear sky chart from 2005-11-06 to 2025-06-10.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	4 5% 2 5% 4 4 4 4 6% 7% 56%	123394
	Night	4 7% 2 5% 3 3 4 3 5% 7% 57%	123785
Transparency	Day	25% 5% 10% 20% 26% 14%	123160
	Night	26% 5% 9% 20% 26% 15%	123606
Seeing	Day	9% 13% 27% 30% 16% 4	15841
	Night	9% 7% 23% 37% 22% 3	26138

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	3 8% 3 6% 4 3 4 3 5% 6% 54%	4098
	11th to 20th	Day	3 7% 2 6% 4 4 4 3 4 5% 58%	4100
	21st to end	Day	5% 9% 2 5% 3 3 3 3 3 5% 59%	4510
February	1st to 10th	Day	4 11% 3 6% 5% 3 3 3 5% 5% 52%	1800
	11th to 20th	Day	5% 11% 3 7% 5% 4 4 3 4 6% 48%	1760
	21st to end	Day	6% 14% 3 6% 4 3 2 3 4 5% 50%	1720
March	1st to 10th	Day	4 9% 2 5% 3 4 4 3 5% 7% 51%	4954
	11th to 20th	Day	3 12% 5% 11% 5% 5% 5% 4 6% 7% 38%	5000
	21st to end	Day	5% 10% 3 7% 5% 5% 5% 4 6% 8% 42%	5486
April	1st to 10th	Day	4 7% 2 5% 5% 4 4 4 5% 6% 53%	2358
	11th to 20th	Day	4 6% 2 5% 5% 4 6% 4 5% 7% 52%	2371
	21st to end	Day	5% 6% 1 5% 4 4 4 4 6% 7% 55%	2400
May	1st to 10th	Day	4 5% 2 6% 4 5% 5% 5% 6% 7% 50%	5869
	11th to 20th	Day	3 3 1 4 4 4 5% 4 7% 8% 57%	5841
	21st to end	Day	2 2 1 3 3 3 4 3 6% 8% 66%	6607
June	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 8% 64%	2788
	11th to 20th	Day	3 2 1 3 3 2 3 2 4 5% 72%	2660
	21st to end	Day	1 2 1 3 3 3 4 4 7% 7% 64%	2653
July	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 6% 68%	4110
	11th to 20th	Day	1 2 1 4 4 5% 7% 6% 10% 11% 50%	4110
	21st to end	Day	4 3 1 4 4 4 5% 4 8% 10% 54%	4454
August	1st to 10th	Day	4 4 2 6% 5% 6% 8% 7% 9% 12% 37%	4092
	11th to 20th	Day	3 3 1 5% 4 5% 6% 6% 6% 10% 52%	3950
	21st to end	Day	2 3 1 5% 5% 5% 7% 6% 8% 9% 47%	4180
September	1st to 10th	Day	6% 3 2 5% 4 4 4 3 6% 7% 55%	2280
	11th to 20th	Day	4 4 2 5% 5% 4 5% 4 5% 6% 56%	2195
	21st to end	Day	5% 3 1 3 3 3 2 3 4 6% 68%	2043
October	1st to 10th	Day	5% 2 1 3 2 2 2 2 3 4 74%	3170
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 6% 6% 56%	3150
	21st to end	Day	5% 4 1 3 2 3 3 3 4 5% 67%	3438
November	1st to 10th	Day	3 4 1 3 3 2 3 3 4 7% 66%	1959
	11th to 20th	Day	4 4 1 3 2 2 3 2 4 6% 69%	1836
	21st to end	Day	5% 7% 2 6% 3 2 3 3 3 4 61%	1600
December	1st to 10th	Day	4 5% 2 3 3 2 2 2 4 7% 66%	2620
	11th to 20th	Day	5% 7% 2 5% 4 3 3 3 5% 7% 56%	3026
	21st to end	Day	5% 10% 3 6% 3 3 3 3 4 5% 56%	4206
January	1st to 10th	Night	3 8% 4 9% 4 3 4 3 4 5% 54%	5867
	11th to 20th	Night	4 8% 2 5% 3 3 3 2 4 4 61%	5880
	21st to end	Night	5% 11% 3 6% 3 3 3 3 4 6% 55%	6468
February	1st to 10th	Night	4 10% 3 5% 3 3 3 3 4 6% 58%	2600
	11th to 20th	Night	6% 9% 3 6% 3 3 4 3 4 5% 54%	2526
	21st to end	Night	6% 11% 3 5% 4 2 3 3 4 6% 52%	1905
March	1st to 10th	Night	5% 11% 3 6% 3 3 4 3 5% 6% 51%	4940
	11th to 20th	Night	5% 12% 4 7% 4 4 4 4 5% 7% 45%	5000
	21st to end	Night	5% 11% 3 7% 4 4 4 4 6% 7% 46%	5489
April	1st to 10th	Night	7% 8% 2 4 4 3 5% 4 5% 6% 53%	2040
	11th to 20th	Night	7% 6% 2 6% 3 4 4 3 5% 5% 54%	1977
	21st to end	Night	4 5% 2 5% 4 3 5% 3 4 6% 59%	2000
May	1st to 10th	Night	4 4 2 4 4 4 4 4 6% 8% 56%	4108
	11th to 20th	Night	4 4 2 4 3 3 4 3 6% 8% 59%	4074
	21st to end	Night	4 3 1 2 2 2 3 2 4 7% 71%	4272
June	1st to 10th	Night	2 2 1 3 2 3 4 3 6% 7% 67%	1596
	11th to 20th	Night	4 3 1 3 2 2 2 2 4 5% 71%	1520
	21st to end	Night	2 2 1 4 3 3 5% 4 7% 7% 63%	1521
July	1st to 10th	Night	2 3 1 4 3 3 4 4 5% 6% 63%	2860
	11th to 20th	Night	1 2 2 4 5% 5% 6% 6% 9% 11% 47%	2860
	21st to end	Night	3 4 1 5% 5% 5% 5% 5% 8% 10% 50%	3109
August	1st to 10th	Night	3 4 2 7% 7% 6% 8% 6% 10% 14% 34%	2847
	11th to 20th	Night	3 4 1 5% 5% 5% 6% 6% 9% 10% 47%	2886
	21st to end	Night	4 5% 2 5% 4 5% 6% 5% 8% 11% 47%	3487
September	1st to 10th	Night	4 4 1 5% 5% 5% 6% 4 6% 7% 53%	1900
	11th to 20th	Night	3 3 2 5% 4 4 4 3 4 6% 61%	1981
	21st to end	Night	6% 3 1 4 2 2 2 2 3 5% 71%	2135
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 75%	3800
	11th to 20th	Night	5% 5% 2 6% 5% 5% 5% 3 5% 5% 55%	3778
	21st to end	Night	5% 5% 2 4 2 2 2 2 3 4 69%	4120
November	1st to 10th	Night	5% 4 1 3 3 2 3 3 4 6% 66%	2340
	11th to 20th	Night	5% 4 1 3 2 2 2 2 3 5% 71%	2535
	21st to end	Night	6% 8% 2 4 3 2 2 2 4 5% 62%	2800
December	1st to 10th	Night	4 5% 1 2 2 2 2 2 3 6% 71%	4570
	11th to 20th	Night	5% 8% 2 5% 3 3 3 2 5% 7% 56%	5181
	21st to end	Night	6% 10% 2 5% 3 3 2 2 3 5% 59%	6813

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 4 12% 30% 21% 3	4099
	11th to 20th	Day	26% 5% 13% 19% 21% 15%	4100
	21st to end	Day	29% 4 7% 21% 29% 11%	4510
February	1st to 10th	Day	34% 4 13% 21% 19% 9%	1800
	11th to 20th	Day	37% 5% 8% 21% 23% 6%	1769
	21st to end	Day	37% 4 6% 16% 29% 8%	1720
March	1st to 10th	Day	28% 7% 7% 20% 32% 7%	4954
	11th to 20th	Day	40% 8% 10% 22% 15% 5%	5000
	21st to end	Day	36% 7% 10% 23% 22% 2	5486
April	1st to 10th	Day	30% 6% 8% 18% 27% 12%	2358
	11th to 20th	Day	29% 6% 9% 17% 27% 12%	2374
	21st to end	Day	25% 6% 9% 21% 29% 9%	2400
May	1st to 10th	Day	29% 4 12% 20% 23% 12%	5869
	11th to 20th	Day	19% 7% 9% 19% 34% 13%	5844
	21st to end	Day	14% 4 6% 17% 40% 19%	6608
June	1st to 10th	Day	17% 5% 7% 17% 31% 23%	2788
	11th to 20th	Day	15% 4 5% 11% 24% 41%	2660
	21st to end	Day	15% 5% 8% 15% 24% 33%	2653
July	1st to 10th	Day	15% 5% 8% 9% 15% 48%	4046
	11th to 20th	Day	23% 7% 10% 25% 26% 10%	4041
	21st to end	Day	22% 8% 12% 23% 14% 20%	4314
August	1st to 10th	Day	34% 6% 23% 16% 10% 11%	4078
	11th to 20th	Day	27% 5% 15% 16% 20% 18%	3989
	21st to end	Day	28% 7% 12% 19% 22% 11%	4179
September	1st to 10th	Day	27% 6% 9% 16% 23% 20%	2280
	11th to 20th	Day	25% 8% 8% 15% 21% 23%	2195
	21st to end	Day	19% 4 7% 15% 36% 19%	2043
October	1st to 10th	Day	16% 3 5% 11% 31% 33%	3170
	11th to 20th	Day	27% 3 5% 21% 32% 12%	3150
	21st to end	Day	20% 3 5% 23% 42% 7%	3438
November	1st to 10th	Day	18% 3 9% 25% 36% 9%	1959
	11th to 20th	Day	18% 3 8% 27% 35% 8%	1836
	21st to end	Day	27% 4 8% 24% 25% 12%	1600
December	1st to 10th	Day	20% 4 9% 34% 28% 5%	2620
	11th to 20th	Day	29% 5% 7% 33% 25% 2	3024
	21st to end	Day	31% 4 12% 23% 22% 8%	4206
January	1st to 10th	Night	32% 5% 9% 29% 21% 5%	5867
	11th to 20th	Night	24% 5% 13% 20% 24% 14%	5880
	21st to end	Night	31% 5% 5% 22% 24% 13%	6468
February	1st to 10th	Night	28% 4 12% 22% 24% 9%	2600
	11th to 20th	Night	32% 4 9% 22% 25% 7%	2527
	21st to end	Night	32% 4 8% 17% 28% 10%	1905
March	1st to 10th	Night	30% 6% 6% 18% 31% 10%	4940
	11th to 20th	Night	36% 7% 8% 19% 23% 7%	5000
	21st to end	Night	33% 7% 9% 26% 21% 3	5489
April	1st to 10th	Night	30% 5% 7% 19% 27% 11%	2040
	11th to 20th	Night	30% 4 7% 16% 28% 14%	1977
	21st to end	Night	25% 4 7% 19% 33% 11%	2000
May	1st to 10th	Night	23% 5% 13% 22% 29% 8%	4105
	11th to 20th	Night	19% 6% 8% 18% 36% 13%	4075
	21st to end	Night	14% 4 5% 14% 39% 25%	4272
June	1st to 10th	Night	16% 4 8% 15% 29% 28%	1596
	11th to 20th	Night	15% 4 6% 11% 19% 43%	1520
	21st to end	Night	16% 5% 9% 13% 22% 35%	1521
July	1st to 10th	Night	20% 6% 7% 9% 8% 49%	2815
	11th to 20th	Night	25% 7% 10% 21% 20% 16%	2806
	21st to end	Night	26% 8% 13% 21% 12% 20%	3011
August	1st to 10th	Night	36% 7% 20% 14% 9% 14%	2838
	11th to 20th	Night	29% 6% 17% 13% 14% 21%	2913
	21st to end	Night	29% 6% 12% 19% 20% 14%	3487
September	1st to 10th	Night	27% 8% 10% 14% 18% 24%	1900
	11th to 20th	Night	23% 6% 8% 17% 20% 25%	1981
	21st to end	Night	19% 3 6% 15% 31% 27%	2135
October	1st to 10th	Night	15% 3 5% 10% 26% 41%	3800
	11th to 20th	Night	31% 3 5% 13% 34% 14%	3778
	21st to end	Night	20% 3 3 19% 42% 12%	4120
November	1st to 10th	Night	20% 4 7% 21% 35% 13%	2340
	11th to 20th	Night	17% 4 6% 25% 37% 11%	2535
	21st to end	Night	25% 3 6% 20% 30% 14%	2800
December	1st to 10th	Night	18% 2 7% 38% 26% 9%	4570
	11th to 20th	Night	28% 4 6% 29% 30% 3	5182
	21st to end	Night	30% 3 10% 24% 24% 9%	6813

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 12% 33% 26% 10% 1	300
	11th to 20th	Day	15% 16% 30% 26% 12% 1	300
	21st to end	Day	10% 14% 34% 28% 12% 2	330
February	1st to 10th	Day	12% 20% 38% 25% 6%	300
	11th to 20th	Day	14% 18% 38% 22% 7%	300
	21st to end	Day	13% 23% 41% 18% 6%	319
March	1st to 10th	Day	16% 22% 30% 22% 8%	500
	11th to 20th	Day	14% 21% 33% 22% 9% 2	500
	21st to end	Day	16% 29% 35% 14% 6% 1	550
April	1st to 10th	Day	11% 24% 32% 23% 8% 2	500
	11th to 20th	Day	15% 26% 34% 18% 7% 1	492
	21st to end	Day	11% 25% 32% 24% 8%	500
May	1st to 10th	Day	12% 20% 36% 23% 6% 1	503
	11th to 20th	Day	9% 16% 33% 26% 14% 2	528
	21st to end	Day	8% 17% 30% 26% 15% 4	653
June	1st to 10th	Day	6% 8% 24% 37% 22% 3	726
	11th to 20th	Day	4 10% 26% 37% 18% 5%	680
	21st to end	Day	3 7% 25% 42% 18% 5%	673
July	1st to 10th	Day	3 3 19% 44% 26% 5%	486
	11th to 20th	Day	3 2 12% 39% 32% 12%	484
	21st to end	Day	6% 1 13% 40% 31% 8%	531
August	1st to 10th	Day	6% 3 17% 42% 26% 7%	487
	11th to 20th	Day	4 3 22% 37% 26% 8%	477
	21st to end	Day	4 2 22% 40% 27% 5%	539
September	1st to 10th	Day	6% 2 23% 37% 26% 6%	490
	11th to 20th	Day	4 8% 29% 37% 18% 4	490
	21st to end	Day	7% 12% 23% 32% 21% 5%	443
October	1st to 10th	Day	11% 15% 21% 20% 23% 10%	300
	11th to 20th	Day	10% 12% 27% 28% 19% 4	300
	21st to end	Day	12% 15% 22% 31% 18% 2	330
November	1st to 10th	Day	11% 14% 28% 29% 16% 2	300
	11th to 20th	Day	7% 12% 32% 33% 13% 3	300
	21st to end	Day	12% 15% 27% 32% 11% 2	300
December	1st to 10th	Day	12% 11% 29% 30% 15% 3	300
	11th to 20th	Day	11% 15% 30% 25% 14% 4	300
	21st to end	Day	20% 15% 27% 29% 8% 1	330
January	1st to 10th	Night	10% 5% 27% 37% 17% 4	800
	11th to 20th	Night	9% 7% 29% 35% 17% 3	800
	21st to end	Night	11% 7% 30% 33% 14% 4	880
February	1st to 10th	Night	10% 7% 35% 34% 12% 2	800
	11th to 20th	Night	11% 8% 35% 34% 10% 2	784
	21st to end	Night	14% 8% 33% 35% 9%	660
March	1st to 10th	Night	11% 10% 31% 34% 12% 2	800
	11th to 20th	Night	9% 9% 29% 33% 19% 2	800
	21st to end	Night	12% 12% 27% 35% 14% 1	880
April	1st to 10th	Night	11% 12% 30% 39% 7% 1	640
	11th to 20th	Night	10% 17% 25% 34% 13% 1	593
	21st to end	Night	9% 12% 32% 36% 12% 1	600
May	1st to 10th	Night	9% 9% 26% 41% 15% 1	600
	11th to 20th	Night	9% 5% 26% 38% 19% 4	591
	21st to end	Night	9% 11% 23% 34% 20% 3	650
June	1st to 10th	Night	3 5% 19% 45% 28% 1	599
	11th to 20th	Night	4 5% 19% 41% 26% 4	570
	21st to end	Night	2 1 18% 44% 31% 3	570
July	1st to 10th	Night	4 2 13% 39% 39% 3	555
	11th to 20th	Night	3 1 8% 35% 46% 7%	552
	21st to end	Night	5% 1 7% 35% 44% 7%	624
August	1st to 10th	Night	4 1 7% 32% 47% 10%	567
	11th to 20th	Night	5% 1 9% 40% 40% 5%	564
	21st to end	Night	5% 1 8% 39% 40% 7%	627
September	1st to 10th	Night	5% 1 11% 39% 38% 5%	570
	11th to 20th	Night	5% 3 16% 40% 31% 5%	651
	21st to end	Night	7% 4 18% 36% 30% 6%	760
October	1st to 10th	Night	8% 8% 22% 35% 25% 3	760
	11th to 20th	Night	6% 4 23% 43% 22% 4	760
	21st to end	Night	7% 8% 23% 37% 21% 5%	836
November	1st to 10th	Night	7% 3 23% 41% 21% 4	780
	11th to 20th	Night	6% 6% 27% 38% 19% 4	885
	21st to end	Night	12% 9% 24% 34% 18% 4	1000
December	1st to 10th	Night	11% 8% 23% 40% 17% 2	1000
	11th to 20th	Night	15% 7% 28% 33% 16% 1	1000
	21st to end	Night	15% 11% 24% 36% 12% 2	1030

Page generated at 2025-06-07 08:28:17. Version ac07

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